1. Field of the Invention
This invention relates generally to the field of chemical and immunochemical assay. More specifically, this invention relates to a system for generation of an interrogating beam and its recovery from a test implement utilizing total internal reflection (TIR), and upon a surface of which a reaction has been caused to occur. The portion of the interrogating beam which interacts with reaction products is the evanescent wave. This wave is an electromagnetic component of light which extends less than a wavelength into a surrounding medium. In a system that uses this waveform as a probe, the light is guided by TIR in a rigid rod or bar or fiber of transparent material which is immersed in a fluid medium with a lower index of refraction. The evanescent wave escapes the transparent material and is altered or modified or attenuated by the reaction in the fluid surrounding the transparent member, and then re-enters the member. The degree and mode of modification is a marker of the reaction which is recovered from the transparent member by directing it to a photodetector. The recovered signal is exquisitely sensitive to subtle reactions in the immediate and intimate region of the rigid transparent member surface.
2. Description of the Prior Art
The sensitivity of the evanescent wave has led to a number of prior art attempts to utilize the phenomena in the detecting of subtle but meaningful reactions in immunochemistry. Lackie, in U.S. Pat. No. 5,152,962, builds upon earlier disclosures of Harte, U.S. Pat. No. 4,133,639, and Hirschfeld, U.S. Pat. No. 4,447,546, to teach a rigid transparent rod or fiber into which an interrogating beam is introduced, and reactions near the surface of which are probed by the evanescent wave. The recovery of the evanescent wave is accomplished by so called EPI-optic coaxial arrangements which employ beam splitting elements to separate the recovered signal in another prior art disclosure, Slovacek, U.S. Pat. No. 5,156,976, teaches a conic internal reflection element which is interrogated by an EPI-formoptical train. Much of the prior art is concerned with coupling both interrogating and recovered signal beams to optical forms suitable for immersion in reactive fluid media. An additional prior art item of interest is Shanks et al., U.S. Pat. No. 4,978,503, which discloses a specifically reactive sample collecting and testing device which utilizes a cavity or cavities each having a dimension small enough to enable sample liquid to be drawn into the cavity by capillary action.
These prior art cases and references, however, fail to fully address the controlled introduction of reactant fluid to the transparent surfaces. Further, the cited prior art references employ EPI-illumination techniques which are by nature inefficient, and significantly, do not allow for inclusion of a blank or control optical beam.
It was in light of the state of the technology as just discussed that the present invention was conceived and has now been reduced to practice.